The cable television (CATV) industry currently transmits video signals over networks which combine fiber optic transmission and coaxial cable. In the typical network architecture, baseband video signals from a number of sources are combined into specific RF frequencies as amplitude modulated vestigial sideband video subcarriers (AM-VSB) and then modulated onto a laser transmitter located at a headend. The fiber optic transmission systems employed for CATV applications today use internally modulated diode lasers. The internal modulation varies the drive current to the diode laser to produce approximately 10 mW of output power. Typically, the 10 mW output is then optically split into three or four outputs and distributed on fiber into the cable feeder plant to three or four nodes as shown in FIG. 1. Each node converts the optical signal to an electrical signal which is then further distributed over a standard tree and branch coaxial cable network to reach approximately 500 homes per node. This network architecture effectively divides the bandwidth of a single laser transmitter between 1500 to 2000 homes, thus limiting the bandwidth per home.
Increased demand for bandwidth to provide new services such as enhanced pay per view, interactive video, and video on demand requires a larger number of channels per node. A desirable network architecture would include the following characteristics:
low cost per home PA1 ability to address target markets PA1 ability to be configured for two-way interactive video services PA1 high reliability
A continuing need exists for further improvements in fiber optic transmission systems that will accommodate these various objectives.